Art of impregnation



Oct. 27, 1936. H. WATERMAN ART OF IMPREGNATION Filed Oct. 18, 1954 INVENTOR Hark/"i lI Zzierfim I ATTORNEYS Patented Oct. 27, 1936 PATENT, OFFICE ART OF IMPREGNATION Herbert Waterman, Wantagh, N. Y., assignor to Aerovox Corporation, poration of New York Application October 18,

16 Claims.

My present invention is concerned with the impregnation of materials for electrical purposes and has specific application to electrostatic wax or oil-impregnated condensers, whether of the enrolled or stacked type, involving absorbent interspacers of paper or other materials.

As conducive to a clear understanding of the invention, itis noted that disturbing variations in the power factor and break-down voltage of condensers, produced apparently by identical impregnation cycles have heretofore commonly occurred during actual service of such condensers. These variations are largely revealed by test of the electrical characteristics of condensers immediately after their manufacture. However, condensers with apparently identical initial characteristics show wide variations in the length oi! their useful life in service. These variations may be accounted for not only by fortuitous differences in materials, but also by fortuitous irregularities and variations as to drying, temperature and other factors in the process of impregnation.

The presence of even slight quantities of moisture in impregnation materials, especially of condensers, as is wellknown, has harmful effects on the operation. If even a minute residue of moisture is present, the condenser develops leakage, it is apt to break down on surge and, in general, has a shortened life.

Due to the fact that paper is a more or less colloidal substance, as are Cellophane and other cellulosic tissues, an attempt to de'siccate to the point of absolute dryness involves complications, since while pure alpha cellulose is a comparatively stable substance, degradation thereof, once begun in the attempt to completely dry it, proceeds quite rapidly.

Difliculties are encountered in ascertaining complete dryness of paper or other cellulosic material, particularly while within the drying chamber, and an attempt to remove the condenser section from the chamber to determine whether it is free from water, would be defeated by the avidity with which the partially or wholly dried sheet would re-absorb moisture from the atmosphere. The material has the optimum condition of dryness for condensers when its dielectric properties are greatest.

It is an object of the present invention to afford a method of controlling the cycle for impregnating any material for electrical purposes and especially electrostatic condensers with spacers of paper or any other material which has properties similar to those of cellulose, to assure Brooklyn, N. Y., a cor- 1934, Serial No. 748,969 (CI. 91-70) According to my invention, there is no attempt directly to measure the dryness of the material, [but the method of control involves continuing the drying until some controlling electrical property reaches the optimum value for the desired purpose. A preferred control is the test that any particular insulator has been brought to its optimum degree of excellence when the product of its electrostatic capacity and its insulation resistance has a maximum value. Another control is the test of attaining the optimum degree of excellence by carrying on the drying until the power factor of the material reaches a minimum.

Accordingly, the method involves a measurement of capacity and insulation resistance of one or more of the units in the course of the impregnation cycle and determining the completion of the drying phase of the cycle, not by measuring the time interval of operation, but by introducing the impregnating medium shortly after the said product of capacity and resistance has reached a sustained maximum value.

The method as applied to condenser impregnation is readily carried into execution by extending electrical leads from one or more condenser sections within any known type of impregnating tank through a vacuum tight bushing, preferably in the hinged cover of the tank, for connection thereto of electrical instruments at the exterior of the tank, to determine, as the impregnating cycle progresses, the product of capacity and insulation resistance.

Since in practice, the temperature in the conventional impregnation, in which a multiplicity of condenser sections are concurrently impregnated, may not be strictly uniform throughout all regions of the tank, it is preferable to extend electrical leads from condenser sections located at various portions of the tank, the measurements' being preferably made on said various condenser sections in parallel, as the cycle progresses, to obtain a fair average of the readings on various condenser sections being subjected to the cycle. The tank should be preferably of such character, ascertained by actual test, that the optimum condition of the insulators in various parts of the tank is reached at nearly the same time, the interval between the first unit and the last unit to reach said condition to be not greater than one-half hour.

The method in its broadest aspects is applicable for comparative tests in the selection of that cellulosic tissue, or other hygroscopic material, most suitable for use in a condenser or other electrical apparatus.

The product resulting from the method herein claimed is made the subject of a divisional application filed September 15, 1936 under Serial No. 100,842.

A specific method for carrying out the control as applied to electrostatic condensers will now be set forth in connection with the accompanying drawing showing desirable apparatus for the purpose.

Fig. 1 shows a diagrammatic view of an impregnating installation with parts of the impregnating tank broken away to disclose the interior construction, and

Fig. 2 is a view on a greatly enlarged scale of the detail of the vacuum tight bushing, through a which the leads for making the respective measurements extend to the exterior.

Referring now to the drawing, the impregnat ing material is stored in a conventional reservoir Ill equipped with a drain ii and connected through a gate valve I! to the bottom of the generally conventional impregnating tank i3.

The impregnating tank I! presents a hollow wall ll serving as a steam jacket and has an inlet pipe I! above the steam Jacket to which air under pressure may be applied to the interior of the tank by way of valve I6 or alternatively, vacuum may be applied by way of valve H.

The tank has the usual hinged cover l8 adapted to be clamped closed for hermetic, seal and equipped with the usual accessories including a safety valve IS, a recording thermometer 20, and a pressure gauge 2|.

Where electrostatic condenser sections S of the flattened rolled foil and interspacer type are used, these are compressed in metal clamps 22 with metal spacer plates 23 tightened under hydraulic pressure and resting on the bottom of the tank i3. Where condensers wound in cross--' section are used, these are impregnated without the application of mechanical pressure. The construction and arrangement as thus far described and/or illustrated is strictly conventional.

According to the present invention, a metal sleeve 25 extends through the cover and is threaded thereto at 28 at its outer end. An insulating plug 21, preferably of Bakelite", has molded longitudinally therein a plurality, illustratively three metal studs 28, said plug threaded into and closing the lower or inner end of sleeve 25.

Electrical leads 28 to be connected to electrodes of individual sections are preferably brazed to the inner ends of studs 28. Flexible leads 30 attached to the outer ends of studs 28, as at 3|, are adapted to be connected to electrical measuring instruments (not shown). A protecting sleeve 32 threaded into the outer end of sleeve 25 encircles the attached ends of leads 30. Thus, though electrical connections of hermetically sealed condenser sections are made at the exterior of the tank, there is no disturbance of the hermetic seal, the connection at the cover being vacuum-tight.

While in general it is preferred to dispose the electrical metering instrument or instruments at the exterior of the drying and impregnating chamber, it is apparent that such instruments could, within the scope of the invention from its broader aspect, be disposed within such chamher, the latter in that case. being, of course, provided with adequate peep-holes to permit readings to be taken.

The inner ends of the conductors 29 within the tank are preferably connected, as at 33, to the inner or ungrounded foils of condenser sections at different localities of the tank, as illustratively shown in Fig. 1, it being noted that the outer foils that contact plates 23 are then grounded to the wall of the tank. The diversity of temperatures at different localities of the tank is taken into account by my method, but this diversity would be minimized with the use of any combined shelf dryer and impregnator of known type. In making the electrical test, a terminal of the capacity meter and of the ohmmeter would be connected to the protruding lead terminals 30 and the other meter terminal grounded to the tank. Of course, the testing equipment could be connected without grounding, to each electrode of the condenser.

In operation, the condenser sections in their clamps, and with one of the electrical lead connections made from those on which the readings are taken, as set forth, are inserted into the empty tank l3, steam heat is then applied, preferably to the open tank to raise the temperature to that at which the impregnating medium is subsequently to be introduced. In practice, a temperature of 250 degrees F. is frequently desirable.

Thereupon, the cover it of the tank is closed and the heat is continued with application of vacuum. In that operation, air and moisture are removed from the interspacers of the various cohdenser sections. As this operation progresses. readings are made on the capacity meter and ohmmeter (not shown). which are connected to the protruding leads 30. Such readings in practice would be made every fifteen minutes or so, but, if desired, recording instruments might be employed for a continuous reading. The insulation resistance rises very rapidly at the outset and the capacity reading falls quite rapidly but soon reaches a practically constant value. The resistance, after its rapid rise, in time will cease increasing, but since the capacity remains practically constant while the resistance is still increasing, the maximum value of the product of capacity and insulating resistance will depend largely on the peak value of the resistance. Preferably the drying is continued for approximately one half hour after said maximum product has been reached.

The impregnating medium is now admitted into the tank by way of gate valve 12, preferably at the temperature maintained during drying, and the heating is continued until impregnation is completed. To aid in the determination of the com-.- pleteness of said impregnation, capacity readings are made from lead terminals 30 from time to time as the impregnation progresses, and when the capacity has reached its maximum, as appears from a cessation of further rise thereof, the completeness of the impregnation is determined. It is desirable, however, to continue the heating for about fifteen minutes to one half hour after this point has been reached, tomake sure that the impregnation is thorough.

The cooling period now begins, generally under vacuum, and when the impregnating medium is a wax, is preferably continued until the temperature is but slightly above that at which said medium becomes thick or hard. At that point the cover I8 of the tank is opened, the clamps 22 carrying the condenser sections are withdrawn, the leads 29 are disconnected, and the sections removed from the clamps, and thereafter tested, cased and sealed according to conventional practice.

In actual quantity production of condensers. the simple procedure above set forth has led to output of uniformly excellent condenser sections of practically constant low power factor, high break-down characteristics and long life.

Among the spacer materials other than cellulose or paper to which the invention is applicable, and which have properties analogous to those of paper, rendering desirable a determination of optimum moisture content, are Cellophane", varnish films and spacers of organic material generally.

While it is preferred to perform the drying operation first and then to introduce the impregnating medium as above set forth, it will be understood that the invention in its broader aspects may be carried out by admitting the impregnating medium either somewhat before or somewhat after the peak value of the product of capacity and resistance has been reached.

In carrying out the method of the present invention, it is preferred in general, to determine the capacity under current of substantially the frequency of the current supplied to the condenser or other apparatus in actual use. For example, condensers designed for power factor correction or motor starting duty at an operating frequency of 60 cycles, should preferably be measured for capacity according to the present method at substantially that frequency, while condensers to be product of capacity and insulation resistance is a maximum, a reasonable approximation of this result may be obtained by a measurement of the power factor of such paper or material as the drying progresses, the minimum value of such power factor establishing the optimum degree of dryness. The capacity-resistance measure is, however, to be preferred, since its maximum value is considerably sharper than the minimum value of the power factor.

The method set forth is readily applicable as a procedure for testing the electrical quality of materials used for impregnation. The various papers or other materials might be subjected to comparative tests under similar conditions of heat and vacuum and that paper or material showing the highest peak product of insulation resistance and capacity as determined by my method, would be preferred as a spacer for electrostatic condenser or in other electrical apparatus, in which such quality is desired.

It will thus be seen that there is herein dewidely different embodiments could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of impregnating an insulating material subject to degeneration by removal of an excessive amount of water therefrom which consists in withdrawing moisture from said material and measuring an electrical property of said material as the moisture withdrawal progresses and introducing the impregnating material when the measured electrical property reaches substantially the optimum value for the desired purpose.

2. The method of impregnating insulating spacers subject to degeneration by removal of an excessive amount of water therefrom which includes the step of subjecting the same to a drying operation'under heat, while metering an electrical property of said spacing material and continuing the drying until the metered property has reached the optimum value for the required purpose, and thereupon, while the spacer material is kept in the drying environment, introducing impregnating medium thereinto.

3. The method of impregnating insulating spacers subject to degeneration by removal of an excessive-amount of water therefrom, which includes the step of subjecting the same to a drying operation under heat and vacuum, while measuring both the insulation resistance and capacity thereof and continuing such operation until the product of said electrical readings has reached a peak value and thereupon, while maintaining said spacers in the drying environment. introducing impregnating material thereinto.

4. The method of impregnating insulating spacers subject to degeneration by removal of an excessive amount of water therefrom which consists in subjecting the latter to a drying operation under heat and vacuum, while measuring the power factor thereof and continuing such operation until the power factor reaches a minimum, value and thereupon introducing impregnating medium into the spacers.

5. The method of controlling the impregnation cycle ofelectrostatic' condensers with insulating spacers of material subject to degeneration by removal of an excessive amount of water therefrom, which consists in progressively reading an electrical characteristic of one of said condensers as the cycle progresses, ascertaining when in the progress of the cycle said reading shows an optimum value and introducing the impregnating medium at about the time said optimum value has been reached.

6. The method of controlling the impregnation cycle of electrostatic condensers with insulating spacers of material subject to degeneration by removal of an excessive amount of water therefrom, which consists in progressively reading the insulation resistance and the capacity of said condenser as the cycle progresses, ascertaining when in the progress of the cycle, the product of said.readings reaches a maximum, and introducing the impregnating medium at about the time said product has reached its maximum.

7. The method of controlling the impregnation cycle of electrostatic condensers with insulating spacers of material subject to degeneration by removal of an excessive amount of water therefrom. which consists in progressively reading the power factor of one of said condensers as the cycle progresses, ascertaining when in the progress of the cycle said power factor reaches a minimum and introducing the impregnating medium at about the time said power factor attains its minimum.

8. The method of controlling the impregnation cycle of paper spaced electrostatic condensers which consists in electrically connectinga condenser section terminal from within a hermeticnlly sealed chamber to the exterior thereof and with the aid of electrical measuring instruments at the exterior of said chamber, ascertaining when in the progress of the cycle, the product of capacity and insulation resistance of said condenser section reaches a maximum, and shortly thereafter introducing the impregnating medium.

9. The method claimed in claim 8 with the added step of measuring the capacity of the condenser at the accessible terminal as the impregnation proceeds and discontinuing impregnation after said capacity has reached a maximum.

10. The method claimed in claim 8 with the added step of measuring the capacity of the condenser at the accessible terminal as .the impregnation proceeds, and continuing the impregnation for approximately fifteen minutes after said capacity has reached a maximum. 7

11. The method claimed in claim 8 with the use of wax impregnating medium and with the added step of measuring the capacity of the con denser at the accessible terminal as the impregnation proceeds, and continuing the impregnation for approximately fifteen minutes after said capacity has reached a maximum and thereupon cooling the contents oi the container under the application of vacuum thereto until the imprcghating medium is about to harden, and at that point removing the condenser sections from the impregnating chamber.

12. The method of controlling the impregnating cycle of paper spaced electrostatic condensers, which consists in heating a multiplicity of condenser sections within a hermetically sealed chamber and applying vacuum for removal of air and moisture therefrom, while determining, at the exterior of said chamber the product of capacity and insulation resistance of one of said condensensections, and discontinuing the drying operation shortly after rise oi said product ceases. I

13. The method of controlling the air and moisture removal from the paper interspacers of wound electrostatic condensers, which consists in electrically connecting terminals of selected condenser sections for access at the exterior of the hermetically sealed chamber to which heat and vacuum are applied to the sections for removal of air and moisture therefrom, determining the product of capacity and insulation resistance of said sections as the drying operation progresses and introducing the impregnating medium after substantial constancy of said product has been maintained for approximately one-half hour.

14. The method of controlling moisture and air removal from the paper interspacers of wound electrostatic condensers, which consists in establishing electrical connections from one of the condenser sections for access from the exterior oi the hermetically sealed chamber in which the cycle proceeds, conducting within said chamber a cycle including preheating under atmospheric pressure, to substantially the temper ature oi the subsequently applied impregnating medium, then. applying vacuum and heat to the chamber, determining the product of capacity and insulation resistance of said condenser sec tion from the exterior of said chamber as application 01 vacuum and heat proceeds, until the said product maintains substantial constancy in]: an appreciable period, and thereupon introducing the heated impregnating medium into the chamber.

15. The method of controlling the removal of air and moisture from paper spaced electrostatic condensers which consists in disposing a multiplicity oi the condenser sections in a chamber, connecting electric leads irom a few or said condensers at various portions of the chamber through a vacuum tight bushing in said cham ber, measuring the product of capacity and insulation resistance of said connected condensers in parallel as the. drying progresses and introducing the impregnating medium after substan-- tial constancy of said product has been maintained for some minutes.

16. The method of controlling the impregnstion of electrical condensers which consists in subjecting the condenser units including hygroscopic insulating spacers to a drying operation under heat and vacuum while measuring progressively the capacity and insulation resistance of at least one of the condensers being dried, under test current of substantially the frequency of the current to be supplied to the finished com denser in use, and introducing the impregnating medium substantially when the product of capacity and insulation resistance of the tested condenser reaches a maximum.

HERBERT WA'I'ERMAN. 

